This invention relates to a new method and apparatus for sheeting the sail of an ice boat or sail boat. The method and apparatus allows efficient and high performance sheeting of a sail board type sail with a rigid upright mast mount configuration.
The term `sheet` refers to the act of pulling the end of a sail towards the center of the vessel so that the sail becomes more parallel to the lengthwise dimension of the vessel. The amount of sheeting controls the power in the sail and hence, the speed of the vessel.
Typical sail boats for use on either ice or water use a main sail sheeting method which has been around for many years. This sheeting method works by having a pulley system attached to a point near the center of the vessel body and a point on the sail boom. The main sheet line is looped through this pulley system. When the main sheet line is pulled, the distance between the vessel attachment point and the boom attachment point is reduced. This produces both a downward and lateral force on the sail. As the sail becomes closer to being fully sheeted in to the center point, the force from the main sheet becomes more and more downward. This works well with conventional sails at lower speeds as a lateral and downward force is required to keep the shape of the sail and both of these forces act to control the performance of the sail.
Sail board type sails which are sometimes called `Windsurfing` sails, have a different construction than conventional sail boat sails. The sail board type sail has a boom mounted to the mast about 4 to 5 feet above the bottom of the sail. This is about arm-shoulder height when mounted on a sail board. The boom holds the shape of the sail along with the down-haul tension by design, as the sail board sail is mounted to a sail board at only one pivoting location. This is in contrast to a conventional sail which requires main sheet tension to hold the shape of the sail.
Conventional sheeting methods work poorly with sail board type sails in a free standing rigid mount configuration. Since a sail board sail holds its own shape and the boom is mounted significantly above the mast base, conventional sheeting methods provide too much downward force and not enough lateral force. In additions a conventional sheeting method will not allow full sheeting to center of a sail board type sail or even a conventional sail as the downward force begins to dominate when the sail gets near the maximum sheeting location. This has the disadvantage on high speed sailing vessels such as ice boats because at vessel speeds two to three times the wind speed, the apparent wind clocks around to the front of the vessel and the top speed is in part determined by how close to center the sail can be sheeted. The downward force of the sheet also has the disadvantage of tightening the leech of the sail thus not allowing the sail to properly spill wind during gusts.
The prior art for sheeting a sail board type sail, other than the standard use of the boom being hand sheeted by the skipper standing on a sail board, has involved using a long pole attached to the body of the sailing vessel. The end of the pole is located near the boom of the sail. A line from near the end of the pole to the boom end can be shortened by the skipper. This allows the sheeting force to be lateral. However, this has the disadvantage of cost and design complexity as the pole must be very strong because of the significant forces involved. The necessary strength requirement for the pole results in heavyweight or high cost for exotic material.
The applicant of this patent is not aware of any prior art or patents which are fundamentally similar to this invention.